The program features both the domestic lives of the team members and their missions abroad, in addition to the effects their careers have on their home lives, wives and girlfriends. It premiered in the United States on March 7, 2006, on CBS as a mid-season replacement. The second season debuted on September 19, 2006.

The third season started on September 25, 2007, with a hiatus occurring after the 11th episode due to 2007–08 Writers Guild of America strike. The show was picked up for a fourth and final season by CBS on May 12, 2008.[1]

The fourth and final season began on September 28, 2008, and concluded on May 10, 2009. On May 19, 2009, it was announced that, after four seasons and 69 episodes, the series had been canceled by CBS.[2] But on the same day, producers 20th Century Fox Television announced that the reruns of the show would be broadcast in syndication, in stations covering 56 percent of the country already committed to carrying the show, including the Fox Television Stations.[3]

The show purports to describe the daily lives of Delta Force (called "The Unit" in the show) operators during training and operational missions as well as their families back home.

Internationally, The Unit premiered on October 3, 2006, in the United Kingdom on Bravo; on October 11, 2006, in Australia on the Seven Network and on FOX8 and Arena on Foxtel/Austar pay-TV network and now airs on 7Two on Tuesdays at 8:30 pm; on January 11 in Spain on La Sexta; on January 25 in The Netherlands on RTL 5; on March 7 in Germany on Sat. 1; on September 23 in Bulgaria on bTV; on March 9, 2008, in Russia on DTV; and on June 13, 2009, in Vietnam on VTC7-Today TV, in Turkey by TNT, and in Indonesia on Global TV.

The theme music for the first and second season was "Fired Up" by Robert Duncan. Although the show focuses on an Army special ops unit, "Fired Up" is an adaptation of a Marine Corps running cadence called "Fired Up, Feels Good". Duncan also created "Walk the Fire", a 22-second segment used as a theme since season three.

The Unit is based at a fictional army post, "Fort Griffith". The location of Fort Griffith is never explicitly stated, but in Episode 103, a bank statement of the lead character clearly shows an address for Fort Griffith, MO 63021, which puts it a few miles west of St. Louis. Other episodes make clear references to Greenwood, including mentions of Greenwood/Fort Griffith area, and local Greenwood police cars as well as Missouri license plates clearly appear in many episodes. Greenwood, Missouri is a small town located southeast of Kansas City. However the red, white and blue license plate is from the state of Idaho. This license plate can be seen in almost all the episodes. Unit members also wear the shoulder sleeve insignia of the inactivated 24th Infantry Division on their Class A uniforms, as well as the shoulder crest of the 504th Parachute Infantry Regiment, "Strike Hold", currently part of the 1st ABCT of the 82nd Airborne Division. In later episodes, Unit members are shown as wearing the United States Special Operations Command (USSOCOM) patch on their Class A uniforms.

The Unit's immediate chain of command goes to the commanding officer, Colonel Tom Ryan—and, presumably, straight to the President of the United States. It is unknown if this bypasses the Secretary of Defense. Though, in the season 4 episode, "The Spear of Destiny," a side character receives confidential mission information and when questioned on who sent her, replies, "The Secretary of Defense." However in the episode, "The Broom Cupboard" the President gives orders directly to Jonas for a Unit mission.

The wives of The Unit's Alpha Team personnel are given minimal mission or operational information. They are responsible for maintaining the "303rd Logistical Studies Group" cover in all interactions with anyone who is not a Unit family member. Their husbands are, in fact, still performing highly dangerous missions, but they are not permitted to know specifics, such as where their husbands are deployed, what their training routines consist of, how long their assignments will last, or even if their husbands are safe.

If a member of The Unit is killed in action, the actual mode of death is not told to the families. A cover story concurrent with a member of the 303 Logistical Studies Unit is created. The wives themselves are encouraged to form a close, cohesive military family based on the common knowledge and strife this inevitably leads to.

The Unit has an unconventional structure. With the size of a company—approximately 130 operators—it is commanded by a Colonel (companies are usually commanded by Captains; Colonels usually command elements such as brigades or regiments). This is parallel to Delta's structure, which was implemented by Col. Charles Alvin Beckwith. The CO, Colonel Ryan, normally wears a "sanitized" uniform (bearing absolutely no tapes, such as his name, or even U.S. Army, or rank insignia).

Whereas a Special Forces ODA (Operational Detachment—Alpha) is commanded by a Captain, the Unit sends five-man teams into the field under non-commissioned officers, such as the team led by Command Sergeant Major Jonas Blane, The Unit's NCOIC of Alpha Team. It is possible that their soldiers have the same Special Forces specialties as in Army Special Forces. An ODA, formerly known as an "A-Team", has Weapons Sergeants, Engineering Sergeants, Medical Sergeants, Communications Sergeants, etc.

The wives, if suspected of speaking about The Unit's existence, can cause their husbands to be expelled and returned to regular Army service. Colonel Ryan has stated, time and again, that this can ruin a soldier's career, as well as his marriage, and has also stated that he will not hesitate to destroy families in order to preserve The Unit's security. He has also threatened the wives with closing The Unit down, and restarting it somewhere else under another cover—forcing the uprooting of all families involved.

The Unit deploys throughout the world, and both the Army and United States government have the ability to deny the existence of The Unit and any of its members in order to prevent the onset of international incidents. Their uniforms are commonly not standard Army issue, which makes it easier to deny their connection with the US Army if they are killed or captured. They also carry weapons that are not always standard issue and the Unit's personnel are well-familiarized with weapons from around the world and can make themselves look like military personnel from other organizations. Unit members can and are sometimes also working as protection details for U.S. diplomats on visit overseas as well as foreign dignitaries and State Department designated VIPs on U.S. soil; in which cases they are attached to the Diplomatic Security Service and do carry the official DSS Special Agent badge.

The Unit's members will frequently use code names such as Snake Doctor, Dirt Diver, Betty Blue, Cool Breeze and Hammer Head, as well as colors (Mr. White, Green, Blue, Black). These are usually used when working directly with American civilians, other English speakers not trained for emergencies, or on counter-terrorism missions. According to Jonas Blane, the order of precedence for his team after he is disabled, is, from top to bottom: Mack Gerhardt, Charles Grey, Hector Williams†, and Bob Brown based on seniority.

^** There are continuity errors regarding the rank of Jonas Blane. In "Pandemonium, Part 2", Blane states his rank as Command Sergeant Major, his uniform rank is Sergeant Major. In the United States Army, however, soldiers are often laterally transitioned between the ranks depending on their assignments. Command Sergeants Major are also addressed as "Sergeant Major" when in conversation, not "Command Sergeant Major". This is similar to the practice (in the Army) whereby Staff Sergeants or Sergeants First Class are addressed simply as "Sergeant."

^** Although this might have just been dirty talk, a similar continuity error exists regarding the rank of Mack Gerhardt. In the season 1 episode "True Believers" his wife says to him "come here Sergeant Major, and give me a report," but his rank is later established as Master Sergeant. In the final wedding scene of season 4, however, Mack is shown with E-7, or Sergeant First Class, rank on his uniform.

^ While in London in S3:E11 members of the Unit are in London, UK. A vehicle is seen with the license/number plate "VEM 416 75" (8 digits, 2 spaces) featuring the "GB and EU star emblem" preceding it, purporting to be a UK number plate. UK number plates currently have a maximum of 7 digits & 1 space.

According to an interview executive producerShawn Ryan gave to The Futon Critic "[David] Mamet and I and our writers, we came up with a lot of great stuff," Ryan said about his pitch to CBS executives for a potential fifth season. "It was going to be a whole new show in the sense that we were going to be training some young people, Bob was going to be training some people for a whole new organization. Jonas was finally going to be seeing his run end......The final season was going to be, I figured the fifth season was going to be the last... It was going to be a long, sort of final mission for Jonas. He's not medically cleared, Mack has to go in and sort of change the medical records so that Jonas can keep on [going on missions]. We had a whole thing planned, it was going to be good." Jonas would eventually leave the army due to his injuries coupled with combat stress and reunite with Molly. Mack would take over the team but at the end of the series would also leave for a training post after Tiffy becomes pregnant with their third child. Bob would be badly injured in a parachuting accident and join the CIA as their Unit liaison. Ryan would take a demotion to regain control of The Unit whilst Bridget Sullivan would be killed on a mission halfway through the season. Charles Grey would take over as team leader with Sam McBride as his deputy training replacements for the personnel they have lost.

Other storylines would include the recruitment of more female members, the team being hounded by human rights campaigners intent on bringing them to trial for their actions, the CIA creating its own rival commando force as a mirror image of The Unit, the search for a mole within the organization leaking information to the highest bidder, the Army's treatment of soldiers suffering debilitating injuries and combat stress and Sam McBride confiding to Bridget Sullivan that he is the Unit's first gay member.[7][8]